diff --git a/src/lib_shell/mempool_worker.ml b/src/lib_shell/mempool_worker.ml
index f26bb792e..40a3bedb8 100644
--- a/src/lib_shell/mempool_worker.ml
+++ b/src/lib_shell/mempool_worker.ml
@@ -51,7 +51,7 @@ module type T = sig
   val shutdown : t -> unit Lwt.t
 
   (** parse a new operation and add it to the mempool context *)
-  val parse : t -> Operation.t -> operation tzresult
+  val parse : Operation.t -> operation tzresult
 
   (** validate a new operation and add it to the mempool context *)
   val validate : t -> operation -> result tzresult Lwt.t
@@ -227,62 +227,58 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
   (* parsed operations' cache. used for memoization *)
   module ParsedCache = struct
 
-    type t = {
-      table: operation tzresult Operation_hash.Table.t ;
-      ring: Operation_hash.t Ring.t ;
-    }
+    type t = operation tzresult Operation_hash.Table.t
 
-    let create () : t = {
-      table = Operation_hash.Table.create Static.max_size_parsed_cache ;
-      ring = Ring.create Static.max_size_parsed_cache ;
-    }
+    let encoding =
+      (Operation_hash.Table.encoding
+         (Error_monad.result_encoding operation_encoding))
+
+    let create () : t =
+      Operation_hash.Table.create 1000
 
     let add t raw_op parsed_op =
       let hash = Operation.hash raw_op in
-      Option.iter
-        ~f:(Operation_hash.Table.remove t.table)
-        (Ring.add_and_return_erased t.ring hash);
-      Operation_hash.Table.replace t.table hash parsed_op
+      Operation_hash.Table.replace t hash parsed_op
+
+    let mem t raw_op =
+      let hash = Operation.hash raw_op in
+      Operation_hash.Table.mem t hash
 
     let find_opt t raw_op =
       let hash = Operation.hash raw_op in
-      Operation_hash.Table.find_opt t.table hash
+      Operation_hash.Table.find_opt t hash
 
     let find_hash_opt t hash =
-      Operation_hash.Table.find_opt t.table hash
+      Operation_hash.Table.find_opt t hash
 
     let rem t hash =
-      (* NOTE: hashes are not removed from the ring. As a result, the cache size
-       * bound can be lowered. This is a non-issue because it's only a cache. *)
-      Operation_hash.Table.remove t.table hash
+      Operation_hash.Table.remove t hash
 
   end
 
   (* validated operations' cache. used for memoization *)
   module ValidatedCache = struct
 
-    type t = (result * Operation.t) Operation_hash.Table.t
+    type t = result Operation_hash.Table.t
 
     let encoding =
-      let open Data_encoding in
-      Operation_hash.Table.encoding (
-        tup2
-          result_encoding
-          Operation.encoding
-      )
+      Operation_hash.Table.encoding result_encoding
 
     let create () = Operation_hash.Table.create 1000
 
     let add t parsed_op result =
       Operation_hash.Table.replace t parsed_op.hash result
 
+    let mem t parsed_op =
+      Operation_hash.Table.mem t parsed_op.hash
+
     let find_opt t parsed_op =
       Operation_hash.Table.find_opt t parsed_op.hash
 
     let iter f t =
       Operation_hash.Table.iter f t
 
-    let to_mempool t =
+    let to_mempool t parsed_cache =
       let empty = {
         Proto_services.Mempool.applied = [] ;
         refused = Operation_hash.Map.empty ;
@@ -297,40 +293,44 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
             op.Operation.proto in
         { Proto.shell = op.shell ; protocol_data } in
       Operation_hash.Table.fold
-        (fun hash (result,raw_op) acc ->
-           let proto_op = map_op raw_op in
-           match result with
-           | Applied _ -> {
-               acc with
-               Proto_services.Mempool.applied =
-                 (hash, proto_op)::acc.Proto_services.Mempool.applied
-             }
-           | Branch_refused err -> {
-               acc with
-               Proto_services.Mempool.branch_refused =
-                 Operation_hash.Map.add
-                   hash
-                   (proto_op,err)
-                   acc.Proto_services.Mempool.branch_refused
-             }
-           | Branch_delayed err -> {
-               acc with
-               Proto_services.Mempool.branch_delayed =
-                 Operation_hash.Map.add
-                   hash
-                   (proto_op,err)
-                   acc.Proto_services.Mempool.branch_delayed
-             }
-           | Refused err -> {
-               acc with
-               Proto_services.Mempool.refused =
-                 Operation_hash.Map.add
-                   hash
-                   (proto_op,err)
-                   acc.Proto_services.Mempool.refused
-             }
-           | _ -> acc
-        ) t empty
+        (fun hash result acc ->
+           match ParsedCache.find_hash_opt parsed_cache hash with
+           (* XXX this invariant should be better enforced *)
+           | None | Some (Error _) -> assert false
+           | Some (Ok op) -> begin
+               match result with
+               | Applied _ -> {
+                   acc with
+                   Proto_services.Mempool.applied =
+                     (hash, map_op op.raw)::acc.Proto_services.Mempool.applied
+                 }
+               | Branch_refused err -> {
+                   acc with
+                   Proto_services.Mempool.branch_refused =
+                     Operation_hash.Map.add
+                       hash
+                       (map_op op.raw,err)
+                       acc.Proto_services.Mempool.branch_refused
+                 }
+               | Branch_delayed err -> {
+                   acc with
+                   Proto_services.Mempool.branch_delayed =
+                     Operation_hash.Map.add
+                       hash
+                       (map_op op.raw,err)
+                       acc.Proto_services.Mempool.branch_delayed
+                 }
+               | Refused err -> {
+                   acc with
+                   Proto_services.Mempool.refused =
+                     Operation_hash.Map.add
+                       hash
+                       (map_op op.raw,err)
+                       acc.Proto_services.Mempool.refused
+                 }
+               | _ -> acc
+             end)
+        t empty
 
     let clear t = Operation_hash.Table.clear t
 
@@ -365,7 +365,7 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
         parameters : parameters ;
       }
 
-    type view = { cache : Cache.t }
+    type view = { cache : ValidatedCache.t }
 
     let view (state : state) _ : view = { cache = state.cache }
 
@@ -374,7 +374,7 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
       conv
         (fun { cache } -> cache)
         (fun cache -> { cache })
-        Cache.encoding
+        ValidatedCache.encoding
 
     let pp ppf _view =
       Format.fprintf ppf "lots of operations"
@@ -491,10 +491,10 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
   (* memoization is done only at on_* level *)
   let on_validate w parsed_op =
     let state = Worker.state w in
-    match Cache.find_validated_opt state.cache parsed_op with
+    match ValidatedCache.find_opt state.cache parsed_op with
     | None | Some (Branch_delayed _) ->
         validate_helper w parsed_op >>= fun result ->
-        Cache.add_validated state.cache parsed_op result;
+        ValidatedCache.add state.cache parsed_op result;
         (* operations are notified only the first time *)
         notify_helper w result parsed_op.raw ;
         Lwt.return result
@@ -511,6 +511,10 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
     Chain.data chain_state >>= fun {
       current_mempool = _mempool ;
       live_blocks ; live_operations } ->
+    (* remove all operations that are already included *)
+    Operation_hash.Set.iter (fun hash ->
+        ParsedCache.rem parsed_cache hash
+      ) live_operations;
     Lwt.return {
       validation_state ;
       cache = ValidatedCache.create () ;
@@ -523,11 +527,11 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
   let on_close w =
     let state = Worker.state w in
     Lwt_watcher.shutdown_input state.operation_stream;
-    Cache.iter_validated (fun hash _ ->
+    ValidatedCache.iter (fun hash _ ->
         Distributed_db.Operation.clear_or_cancel
           state.parameters.chain_db hash)
       state.cache ;
-    Cache.clear state.cache;
+    ValidatedCache.clear state.cache;
     Lwt.return_unit
 
   let on_error w r st errs =
@@ -568,12 +572,11 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
     Worker.push_request_and_wait t (Request.Validate parsed_op)
 
   (* atomic parse + memoization *)
-  let parse t raw_op =
-    let state = Worker.state t in
-    begin match Cache.find_parsed_opt state.cache raw_op with
+  let parse raw_op =
+    begin match ParsedCache.find_opt parsed_cache raw_op with
       | None ->
-          let parsed_op = parse_helper t raw_op in
-          Cache.add_parsed state.cache raw_op parsed_op;
+          let parsed_op = parse_helper raw_op in
+          ParsedCache.add parsed_cache raw_op parsed_op;
           parsed_op
       | Some parsed_op -> parsed_op
     end
@@ -588,7 +591,7 @@ module Make(Static: STATIC)(Proto: Registered_protocol.T)
       (Proto_services.S.Mempool.pending_operations RPC_path.open_root)
       (fun w () () ->
          let state = Worker.state w in
-         RPC_answer.return (Cache.to_mempool state.cache)
+         RPC_answer.return (ValidatedCache.to_mempool state.cache parsed_cache)
       )
 
   let monitor_rpc_directory : t RPC_directory.t =
diff --git a/src/lib_shell/mempool_worker.mli b/src/lib_shell/mempool_worker.mli
index a485641b7..f5c33e8c9 100644
--- a/src/lib_shell/mempool_worker.mli
+++ b/src/lib_shell/mempool_worker.mli
@@ -51,8 +51,8 @@ module type T = sig
   val create : limits -> Distributed_db.chain_db -> t tzresult Lwt.t
   val shutdown : t -> unit Lwt.t
 
-  (** parse a new operation and add it to the mempool context *)
-  val parse : t -> Operation.t -> operation tzresult
+  (** parse a new operation *)
+  val parse : Operation.t -> operation tzresult
 
   (** validate a new operation and add it to the mempool context *)
   val validate : t -> operation -> result tzresult Lwt.t